Discussed here. If they’re any similar to the Highlander clans, the northern hill clans follow the custom of fictive kinship, in which the smallfolk of House Wull are considered Wulls themselves, with certain rights that pertain to that.
Now, that doesn’t mean the distinction between high and low is less relevant – being a crofter in the Highlands was not an easy life, even before the enclosure movement and the Industrial Revolution – just that it takes different forms.